1. Field of the Invention
This invention is in the fields of air fuel mixture stratifiers and igniters for internal combustion engines of the piston and cylinder type, wherein a jet of air fuel mixture can be used to create a stratified principal air fuel mixture in the combustion chamber of the engine cylinder.
2. Description of the Prior Art
The Hesselman engine combustion process, and the more recent Texaco combustion process, are examples of early prior art air fuel mixture stratifiers, which created a stratified principal air fuel mixture in the engine combustion chamber. Descriptions of examples of these prior art mixture stratifier schemes are presented in the following references:
In these prior art Texaco combustion processes, a jet of liquid fuel was injected into the engine combustion chamber, near the end of the compression stroke. The air inside the engine cylinder was set into rotary motion during intake, by use of shrouded intake valves, or specially oriented intake ports and manifolds. The liquid fuel spray was carried by the rotating air into which it was injected, toward a spark igniter. When this stratified air fuel mixture reached the spark, evaporated portions of the fuel, diffused into the surrounding air, were ignited by the spark, and a burning zone was thus created. The heat generated in this burning zone, evaporated those fuel portions unevaporated at the time of spark ignition and subsequent interdiffusion of air and thusly evaporated fuel maintained the burning zone, until most of the injected liquid fuel was burned. This burning process somewhat resembles that of a conventional liquid fueled oil burner, except that it is carried out intermittently and at high pressure.
Since air fuel vapor mixture is burned very shortly after being created, time is not available for expiration of the compression ignition delay period, which leads to engine knock. Thus one principal advantage of the Texaco combustion process was that high engine compression ratio, and hence high engine efficiency, could be achieved while using fuels of low octane number, and hence low knock resistance. Such low octane number fuels are generally of lower cost than high octane number fuels.
Engine torque was adjusted, for this Texaco combustion process, by proportionally adjusting the liquid fuel quantity injected into the engine cylinder, using fuel injection pumps and nozzles very similar to diesel engine injection pumps and nozzles. Since a stratified mixture was used, the air quantity inside the engine cylinder did not require adjustment, and an intake manifold throttle valve was not used. In consequence, the engine efficiency losses due to intake air throttling were avoided. Hence another principal advantage of the Texaco combustion process, was that high engine efficiency could be obtained at low engine torque since the usual throttling and consequent pumping power loss was avoided.
Liquid fuel, unevaporated at the start of burning, becomes surrounded by very hot burned gases, essentially devoid of oxygen. Rapid evaporation of liquid followed, but in the absence of oxygen, this evaporated fuel produced a high yield of soot particles, in a manner similar to soot production in diesel engines. Appreciable portions of this soot survives to exhaust to create an undesirable exhaust soot emission.
The injected liquid fuel volume, being much smaller than the air volume needed for burning, it is difficult to distribute the liquid spray particles uniformly throughout the cylinder air mass. In consequence the available cylinder air mass is incompletely utilized for burning. For this reason a larger engine displacement is needed, resulting in increased engine weight and cost than for a comparable conventional gasoline engine.
The liquid fuel is injected at high pressure, and the fuel injector must withstand subsequent peak combustion pressures and the high heat transfer rates which follow. The fuel injection equipment is thus essentially similar to that used with conventional diesel engines and is expensive.
These then are the principal disadvantages of the Texaco combustion process; that exhaust soot is emitted, that a larger engine displacement is needed, and that expensive fuel injection equipment is required. It would be desirable to have available an engine system capable of realizing the knock suppression and reduced pumping friction loss characteristics of this Texaco combustion system, but possessing reduced soot emissions, better air utilization, and lower cost fuel injection apparatus.
3. Definitions
The term piston internal combustion engine is used herein and in the claims to mean an internal combustion engine of the piston and cylinder type, with connecting rod and crankshaft or equivalent, such as the Wankel engine type, or opposed piston type engines. Each piston internal combustion engine comprises at least one combined means for compressing and expanding gases, each combined means comprising: an internal combustion engine mechanism comprising a variable volume chamber for compressing and expanding gases, and drive means, such as a connecting rod and crankshaft, for driving said internal combustion engine mechanism and varying the volume of said chamber through repeated cycles. Each variable volume chamber comprises a combustion chamber end at the minimum volume position of the variable volume.
Each variable volume cycle comprises a compression time interval, when said variable volume is sealed and decreasing, followed by an expansion time interval, when said variable volume is sealed and increasing, these two time intervals together being a compression and expansion time interval.
Each combined means for compressing and expanding further comprises intake means for admitting reactant gases into said variable volume chamber prior to each compression time interval and exhaust means for removing reacted gases from said variable volume chamber after each expansion time interval.
Each variable volume cycle further comprises an exhaust time interval, when said variable volume is opened to said exhaust means, followed by an intake time interval, when said variable volume is opened to said intake means, these two time intervals being an exhaust and intake time interval; said exhaust and intake time interval following after a preceding expansion time interval and preceding a next following compression time interval. For a four stroke cycle piston internal combustion engine each separate time interval occupies approximately one half engine revolution and thus one stroke of the piston. For a two stroke cycle piston internal combustion engine the expansion time interval together with the exhaust time interval occupy approximately a half engine revolution and one piston stroke, and an intake time interval followed by a compression time interval occupy the next following half engine revolution and piston stroke.
A piston internal combustion engine further comprises a source of supply of reactant gas containing appreciable oxygen gas to each said intake means for admitting reactant gases into said variable volume chamber.
A piston internal combustion engine further comprises an igniter for igniting fuel air mixtures contained within the combustion chamber of the variable volume chamber. Various types of igniters can be used, such as timed electric sparks, glow plugs, compression ignition via adequate engine compression ratio, and combinations of these igniters.
The combustion time interval is that portion of the compression and expansion time interval when ignition and burning of the air fuel mixture in the engine cylinder is intended to take place. For reasons of engine efficiency, this combustion time interval is preferably intended to occur when the variable volume chamber is at or near to its minimum volume, during or following a compression time interval.
The term reactant gas containing appreciable oxygen gas is used herein and in the claims to mean a reactant gas having a ratio of oxygen gas to inert gases at least about equal to that for air, and which may additionally comprise a principal engine fuel.
Many different types of fuels are suitable for use on internal combustion engines equipped with fuel air mixers and proportioners of this invention. The following are some examples of suitable commercial fuels:
In principle, any fuel which, when mixed with air or other oxygen rich gas in suitable proportions, can be spark ignited or compression ignited, is suitable for use with the invention described herein. The term stoichiometric mixture ratio is used herein and in the claims to mean that mixture ratio of fuel to oxygen which, if fully reacted, would produce only complete combustion products.
Hydrocarbon fuels are spark ignitable and flammable over a moderate range of mixture ratios, both fuel leaner and fuel richer than the stoichiometric mixture ratio. Most hydrocarbon fuels are also compression ignitable and over a wider range of mixture ratios than their spark ignitable mixture ratio range, provided adequate compression is used. Hydrocarbon fuels, undergoing compression ignition, exhibit a compression ignition time delay period, between application of compression and occurrence of ignition. This compression ignition time delay period is shortest at mixture ratios at and near to stoichiometric, becoming longer for mixture ratios both leaner and richer than stoichiometric. The octane number, or cetane number, of a hydrocarbon fuel is an indicator of its compression ignition time delay characteristics, longer time delay being indicated by higher octane number or lower cetane number.